Drop phasing in ink drop writing apparatus

ABSTRACT

IN AN APPARATUS OF THE TYPE WHEREIN INK UNDER PRESSURE IS APPLIED TO A NOZZLE WHICH IS VIBRATED, AND THE INK EMITTED BY THE NOZZLE THEREAFTER BREAKS DOWN INTO INK DROPS WHICH ARE CHARGED IN A CHARGING TUNNEL IN RESPONSE TO VIDEO SIGNALS, MEANS ARE PROVIDED, IN ACCORDANCE WITH THIS INVENTION, FOR SENSING WHETHER OR NOT THE INK DROPS ARE MADE TO OCCUR WITH THE PROPER PHASE TO ASSUME THE PROPER CHARGE, AND IF NOT, TO CORRECT THE PHASE TO ASSUME THE VIBRATION OF THE NOZZLE WHEREBY THE INK DROP PHASING AND CHARGING ARE CORRECTED.

Feb. 9, 1971 J. J. STONE, ET AL 3,562,761

DROP PHASING IN INK DROP WRITING APPARATUS Filed Dec. 23 1968 2Sheets-Sheet l I ,26 3o PRIOR 1 SVNC. Q E

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log, 92 PHASE- DVELAV i CHANGE. EFQCU NETWORK 46E 961 40 Q L l VIDEOSYNC. I I TEST5I6 a CIRCUIT 20 V l I04 98 I r2 --Q5TE9TQE \I Q TINVIN'IURS JOSEPH J. STONE s N L /Ncswr zili/scHop/ lsourzcE BY o wUnited States Patent 3,562,761 DROP PHASING IN INK DROP WRITINGAPPARATUS Joseph J. Stone, Glenview, and Vincent E. Bischolf, RiverGrove, Ill., assignors to A. B. Dick Company, Chicago,

111., a corporafion of Illinois Filed Dec. 23, 1968, Ser. No. 786,277Int. Cl. G01d 15/18 U.S. Cl. 34675 5 Claims ABSTRACT OF THE DISCLOSUREIn an apparatus of the type wherein ink under pressure is applied to anozzle which is vibrated, and the ink emitted by the nozzle thereafterbreaks down into ink drops which are charged in a charging tunnel inresponse to video signals, means are provided, in accordance with thisinvention, for sensing whether or not the ink drops are made to occurwith the proper phase to assume the proper charge, and if not, tocorrect the phase of the vibration of the nozzle whereby the ink dropphasing and charging are corrected.

BACKGROUND OF THE INVENTION This invention relates to apparatus forwriting with ink drops which are charged by a video signal and directedthrough an electric field to be deflected in accordance with the charge,and more particularly to improvements therein.

An ink drop writing apparatus has been developed wherein ink is appliedunder pressure to a nozzle. The nozzle is vibrated in response to asynchronizing signal which is also used for synchronizing video singals.The vibrated nozzle causes an ink jet, which is emitted therefrom tobreak up into uniform drops at a distance away from the tip of thenozzle. The rate of such drop formation is determined by the vibrationrate. A means for charging each drop is provided at the location atwhich the ink stream begins to break into drops. This means usually is aconductive tube or cylinder. Video signals are applied between thenozzle and the cylinder in response to which a drop assumes a chargedetermined by the amplitude of the video signal at the time that thedrop breaks away from the jet stream.

The drop thereafter passes through a fixed electric field, as a resultof which it is deflected by an amount determined by the amplitude of thecharge on the drop. At the boundary of the electric field there ispositioned a writing medium upon which the drop falls. Since thedeflection of the drop is determined by the charge on the drop, thearrangement enables one to write information with the ink which iscarried by the video signal.

As previously stated, at the time that a drop separates from the fluidstream, the drops are charged by electrostatic induction. If the fieldestablished by the video signal is maintained while the drop separates,the drop will carry a charge determined by this video signal. Obviously,if the video signal is in the process of rising or falling or is notpresent at the time the drops separate, the charge on the drop will notbe that of the video signal. In order to place specific charges on givendrops, one must know when drop separation is occurring or the phasing ofthe drop formation relative to the video signal. In the absence ofcontrol over drop separation time, because of unpredictable phasechanges in the ink drop formation, the uniformity and the fidelity ofthe printing are affected adversely.

In an application 'by Keur and Vorne, Ser. No. 712,800 filed Mar. 13,1968, now Pat. No. 3,465,350, which is assigned to this assignee, thedetection of the ink drop 3,552,761 Patented Feb. 9, 1971 phasing wasaccomplished by placing a detector at the location to which the inkdrops should be deflected if they were properly charged. If the inkdrops are improperly charged, indicating an incorrect ink drop formationphase, no signal would be obtained from the detector and the phase ofthe vibration of the nozzle would be shifted which would correct thephase of formation of the ink drops thereby the ink drops becomeproperly charged.

In an application by Keur and Dahl, Ser. No. 712,808 filed Mar. 13,1968,now Pat. No. 3,465,351, and also assigned to this assignee, anotherarrangement for phase detection and correction of ink drop formation isdescribed. Here, the frequency of the video signal relative to thefrequency of the generation of the ink drops is made such that, if thephasing is correct, alternate ink drops receive a charge. During thetransit time between the charging tunnel and the phase detector, thereis a tendency for a charged ink drop to merge with the adjacentuncharged ink drop. As a result a frequency detector may be employed. Ifthe drops are generated in the proper phase, the frequency of the dropsarriving at the drop detector is half the. frequency at which the dropsare generated. If the phase relationships are incorrect then the dropswhich are received by the detector will have a somewhat randomfrequency.

While the technique just described for detecting the phasing of the inkdrops operates satisfactorily, the clumping or gathering of the adjacentink drops requires a rather long time of flight of the ink drops inorder to make absolutely certain that this occurs. It was also foundthat the charge on the drops had to be substantial. Upon analysis it wasfound that the reason for the gathering of the adjacent ink drops wasbecause the drop charging process imparted a slight velocity change tothe charged droplets as compared to the uncharged droplets. As thecharged droplet approaches the uncharged droplet the attractive forcebetween them accelerates the clumping. Without the velocity modulationthe forces between droplets are balanced and no tendency to clump wouldoccur.

OBJECTS AND SUMMARY OF THE INVENTION An object of this invention is theprovision of an improved system for enabling detection and correction ofincorrect ink drop phasing. This is achieved by providing test videosignals for charging ink drops which operate to charge two adjacent inkdrops and then do not charge the succeeding two ink drops. As a resultthe two adjacent charged ink drops are positively driven in oppositedirections due to the repelling effects of their charges whereby theyclump with the adjacent uncharged drops. As a result, if the phasing ofthe drops is proper, they generate a a strong fixed frequency signal atthe detector. If the phasing of the drops is improper the fixedfrequency is no longer present. The phasing of the drop formation maythen be changed to provide the proper phasing.

The novel features of the invention are set forth with particularity inthe appended claims. The invention will best be understood from thefollowing description, when read in conjunction with the accompanyingdrawings.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block schematic drawing ofa prior art ink drop writing system.

FIG. 2 is a schematic drawing of a mechanical arrangement for an inkdrop printing system in which this invention may be employed.

FIG. 3 illustrates a series of wave shapes to assist in an understandingof this invention.

FIG. 4 is a block schematic diagram illustrating the electricalarrangement required for this invention.

FIG. is a block schematic diagram of the details of the detector andvideo test signal circuits which are referred to in FIG. 4, and

FIG. 6 illustrates the circuit details of the video logic required withthis invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic drawingof the presently known arrangement which is shown to afford a betterunderstanding of the invention. An ink reservoir 10 provides ink underpressure to tubing 12 which is flexible. An electromechanical transducer14 is usually placed adjacent to or around the tubing. The transducer isdriven in response to signals from a source 16. The transducer serves tovibrate and/ or compress the tubing 12 in the region of the nozzle 18.This results in an ink jet being emitted which at a short distancedownstream breaks up into drops 22 which are formed at a rate determinedby the frequency of the vibration. In the region Where the stream 20breaks down into drops, a charging tunnel 24 is provided. This comprisesa conductive cylinder to which video signals from a video signal source26 are applied. The video signals establish a field within the chargingtunnel so that the. ink drops which are formed therein assume a chargedetermined by the amplitude of the video signal present at the time thedrop separates from the ink jet 20.

Downstream of the charging tunnel there are usually placed a pair ofelectrodes 28 which are connected to a field bias source 30. As aresult, there is established between the electrodes a constant electricfield. The ink drops, which bear charges in accordance with the videosignal, enter this field and are deflected by an amount which isproportional to the amplitude of the charge. This enables intelligentwriting to occur on a writing medium 32, which is moved at somesynchronous rate past the electrodes. Drops which do not bear a videocharge are captured by a tube or trough 34 which is judiciously placedat one side so as to capture these drops. It leads to a waste reservoir36. The paper 32 moves into the plane of the drawing whereby its motion,together with the deflection of the drops, may be used for formingintelligible characters.

In order to write lines of information across a wide sheet of paper, anarrangement such as is schematically represented in FIG. 2 may beemployed. Here, the ink drop writer 40 is attached to a traveling nut 42which is free to move on a journally supported lead screw 44. At the topof the ink drop writer is a nut 46 which is free to slide along a rod48. Accordingly, as the lead screw 44 is rotated in one direction or theother, the ink drop writer will move in a direction dictated by thisrotation along a path parallel to the lead screw.

By ink drop writer is meant a housing which supports the ink reservoir10, tubing 12, transducer 14, nozzle 20, and charging tunnel 24. Thevideo and sync signal sources are placed elsewhere and are connected tothe ink drop writer by wires. The function of the deflection electrodes28 is performed by a pair of spaced plates 41 which extend the path oftravel of the ink drop writer and are placed so that the stream of dropspass therethrough on their way to the paper. A trough (not shown)identical to the tube 34 is provided which extends adjacent the bottomplate.

The paper 50 upon which writing is to occur moves in a directionvertical to the direction of the path of motion of the ink drop writer.A motor 52 has a first shaft 54 extending therefrom to a /2 sector gear56. The motor has a second shaft 58 extending therefrom to a gear box60, which functions to reverse the direction of rotation of the shaft58. This reverse motion is communicated through a shaft 62 to another /2sector gear 64 in which it terminates. The sector gears are cut so thatas the motor rotates the sector gear 56 engages a gear 66 attached toone end of the lead screw to rotate the lead screw 44 so that the inkdrop writer is moved from left to right. When the ink drop writerreaches the right-hand end of the lead screw, the sector gear 56 isdisengaged from the gear 66 and the sector gear 64 engages a gear 68 onthe other end of the lead screw. This results in the lead screw beingrotated in the opposite direction thereby returning the ink drop writer40 to its home position on the left-hand side of the lead screw. Motorcontrol apparatus 70 serves the function of energizing the motor torotate over the interval required for the ink drop writer to make oneround trip path along the lead screw. The motor control then waits untilit receives a signal from a gate, shown in FIG. 4, which enables themotor to again function to cause the ink drop writer to make a roundtrip path.

A sensing switch circuit 72 has a feeler 74 which trips the sensingswitch circuit when the ink drop writer returns to the home position.The sensing switch circuit may be any well known arrangement forgenerating a signal when the feeler 74 is actuated. This can be, forexample, an arrangement for connecting a battery to the terminal 71until the feeler 74 is out of contact with the ink drop writer.

It should be noted that when the ink drop writer is in the home positionthe deflection plates 41 are not present.

In accordance with this invention it is desired to apply a charge withthe test video signal to two adjacent drops, skip the next two drops,then apply a charge to the two adjacent drops that follow. To do this, avideo signal having the wave form 80, as shown in FIG. 3, is required.This wave form is achieved by generating a 33 kHz. rectangular pulsetrain and inhibiting each succeeded two pulses, as indicated by thedotted lines 82 in the wave train. Drops 84, which are generated inphase with the video signal, will assume a charge-uncharge pattern asrepresented by the drops bearing pulses, indicative of the charged dropsand the ones without any sign indicative of no charge.

In accordance with this invention, two adjacent drops have charges.Accordingly, they will repel each other with a rather strong force, oneof the drops being pushed back toward the preceding uncharged drop whilethe other drop is pushed forward toward the succeeding uncharged drop.Since there are no shielding drops between the charged drops, theoperation occurs rather quickly and within a short distance from thecharging tunnel.

As a result, the drop pattern obtained from the combined drops is shownby the drop representations 86. The wave form 88, illustrates the signalwhich is generated by a transducer receiving these drops. Thisrepresents a wave train having a 16.5 kHz. frequency.

When the drops are not formed in phase with the video signal, anuncharged drop pattern arises which produces a signal pulse train 90.The frequency of this signal pulse train is much higher than that of thesignal train 88 thus detection between proper phasing of the formationof the drops and improper phasing of drop formation is rendered veryeasy. It should also be noted that the width of the video signal pulseemployed for charging is made rather narrow, being on the order of 7.5microseconds, so that the likelihood of the charging of drops which arenot in phase with the video signal is considerably reduced.

FIG. 4 is a schematic drawing illustrative of the circuitry required inconjunction with the ink drop forming and charging apparatus. Thosestructures which are shown in FIGS. 1 and 2 and which perform the samefunctions as are described in connection with the description of thesefigures have the same reference numerals applied thereto. The 66 kHz.sync signals are applied from the generator 16 to the phase changenetwork 92, and to the video test signal circuit 94. The phase changenetwork, under control of a phase control network 96, applies 66 kHz.signals in one or the other of two phases to the transducer 14, whichvibrates the nozzle.

The ink stream which is emitted from the nozzle 18 breaks down intodrops within the charging tunnel 24 and receives the video signals,which by induction apply charges to the drops which are formed. Thesedrops fol low a trajectory (without being passed through a pair ofelectrodes 28, as shown in FIG. 1) which causes them to strike a rod 98.This may be a conductive rod, or a rod of piezo-electric material, orsome other transducing material. If the rod is conductive, it collectsthe charges from the charged drops and produces a signal wave train 88,as shown in FIG. 3. If the rod is made of piezo-electric material, asignal wave train 88 is generated. In either case, the signal wave trainis established across a resistor 100 which is then amplified by theamplifier 102. The out- .put of the amplifier is applied to a detectingnetwork 104.

The detecting network determines whether or not a 16.5 kHz. signal ispresent. If it is, then the phase control network 96 is operated tocause the phase change network 92 to switch the phase of the 66 kHz.signal by 180. This causes the drops to be formed by the vibratingnozzle 18 with the 180 shift in phase. As a result, the drops areproperly charged, in the manner illustrated in FIG. 3.

In order to insure that a suflicient number of drops is collected beforethe phase change network is operated, to insure that a good sample isobtained, the output of the sensing switch 72 is applied to a delaycircuit 106. This delays the enabling of the phase control network 96 torespond to the output of the detector 104 until such time as therequired number of ink drops for making a good sample has beencollected.

The detector 98 is supported over a container 99 into which the spentink drops fall.

FIG. shows details of the video test signals circuitry as well as of thedetector, phase control network, and phase change network. The droptransducer 98 applies the output which it generates in response toreceiving drops, to the amplifier 102. The output of the amplifier isapplied to a 16.5 kHz. filter 105. This is a narrow-band filter, passingsignals centered at 16.5 kHz. to integrator 107. The integrator is usedto insure that the signal amplitude being generated is more than thatreceived from an occasional group of drops. The output of the integratoris shaped by a Schmitt trigger circuit 108.

The output of the Schmitt trigger 108 is applied to an inverter 109. Theoutput of the inverter is applied to an AND gate 110. The AND gate alsoreceives a train of pulses from a multivibrator 112. Another input tothe AND gate is that received from the delay circuit 106. It

will be recalled that the sensing switch 72 which detected when thedelay circuit was in its home position delayed the resulting signal toenable a suitable sample of the drops to be collected by the droptransducer 98.

In the presence of an output from the Schmitt trigger 108, the inverter109 inhibits the AND gate 110 with its output. In the absence of aninput to the integrator 107, the inverter 109 output together with anoutput from the delay circuit 106 enable a pulse from the multivibrator112 to pass through the AND gate 110. The AND gate output drives aflip-flop 114 causing it to go from one state to the other. If it is ina state with its Q gutput high then it will be driven to the state whereits Q output is high. If it is in the state where its Q output ishigh,'then its state will be reversed.

The respective Q and 6 outputs of the flip-flop 114 are connected to twoAND gates respectively 116, 118. The output of the 66 kHz. signalgenerator 16 is directly applied to the AND gate 118 and through a phaseinverter 120 is applied as another input to the AND gate 116.

The operation of the circuit arrangement of FIG. 5 should be clear. Theoutput of the Schmitt trigger 108, when present, indicates that thedrops are being formed in phase and therefore inhibits AND gate 110 sothat the flip-flop 114 is not driven. In the absence of a Schmitttrigger output, a pulse from the multivibrator 112 appears at the ANDgate output and drives flip-flop 114 to its opposite stable state. Thiscauses one or the other of the phase select gates 116, 118 to becomeenabled whereby the phase of a 66 kc. signal which is applied to asucceeding OR gate 122, is reversed. The output of the OR gate 122 isapplied to the transducer 14 to be used to vibrate the nozzle and thusdetermine the phase of drop formation.

The output of the delay circuit 106 can also be used to instruct themotor control 70 (shown in FIG. 2) that the end of a sampling period hasoccurred, and that it is time to initiate another writing line. However,to insure that the phase detecting circuitry has operated, the output ofthe integrator 106 and the output of the AND gate are applied to an ORgate 124, the output of which is applied to an AND gate 126. The otherinput to the AND gate is the output delay circuit 106. Accordingly, inthe presence of a delay circuit output together with an output fromeither the Schmitt trigger or the AND gate indicative of the fact thatthe phase detecting network is operated, the signal is applied to themotor control circuit 70 to instruct it to cause the motor to proceed toanother cycle of operation.

The test video signal, as shown in FIG. 3, is generated by applying theoutput of the 66 kc, signal generator 16 to a divider circuit 130, whichmay comprise a flip-flop, which divides the signal by one-half. Theoutput of thee divider circuit is applied to an AND gate 132. This ANDgate is enabled in the presence of a signal from the sensing switch. Itsoutput, consisting of a 33 kHz. signal is applied to video logiccircuits 134. The output of the video logic circuits constitutes thevideo signal having a requisite waveform.

FIG. 6 is a block schematic diagram of the video logic 134. The 33 kHz.pulse is applied to a delay circuit 134 which provides a short delay toenable the circuits to attain steady state after the sensing switch hasoperated. The output of the delay circuit is applied to a dividingflip-flop 136, which in response to the 33 kHz. input provides a 16.5kHz. output. This is applied to a 15 microsecond one shot circuit 138,and to a 7.5 microsecond one shot circuit 140. The output of the 15microsecond one shot circuit is also applied to a second 7.5 microsecondone shot circuit 142. The outputs of the two 7.5 microsecond one shotcircuits are applied to an OR gate 144. The output of the OR gatecomprises the desired video signal.

The 7.5 microsecond one shot circuit is a multivibrator circuit which inresponse to receiving an input pulse provides an output signal pulsewhich is 7.5 microseconds wide. The 15 microsecond one shot circuit alsois a multivibrator which, in response to its input provides an outputwhich is delayed 15 microseconds from its input. This output triggersthe second 7.5 microsecond one shot circuit 142 which provides a second7.5 microsecond pulse 15 microseconds after the commencement of thefirst 7.5 microsecond pulse.

The operation of the circuit just described is to provide two 7.5microsecond pulses whose leading edges are spaced apart 15 microsecondsfor every 16.5 kHz. pulse which is received. This results in the wavetrain which is shown in FIG. 3.

From the foregoing description, it should be appreciated that thisinvention, by charging two adjacent drops and then not charging thefollowing two drops provides a mechanisms whereby the adjacent chargedrops positively repel each other to join with the uncharged drops oneither side of these charge drops. This serves to make the detection ofwhether or not the drops have been generated with the proper phase toreceive the charges, a simple, and binary operation. That is, if thedrops are generated in phase with the video signal and thus are chargedproperly, the phasing of the generation of the drops is left unaifected.If the detection shows the improper drop phasing by the absence of a16.5 kHz. signal, then the phasing of the drop generation is shifted tocorrect for this. This test is made upon the completion of every roundtrip of the ink drop writer and thus proper operation of the ink dropwriter is maintained.

There has accordingly been described and shown herein, a novel anduseful arrangement for insuring that the detection of the phase offormation of ink drops is positive and reliable.

What is claimed is:

1. In an ink drop writing system of the type wherein ink under pressureis delivered to a nozzle, an electromotive transducer vibrates thenozzle, synchronizing signals from a source drive the transducer, thenozzle emits an ink jet which breaks into drops in synchronism with thevibration of the nozzle, a charging tunnel is positioned in the regionat which the ink jet breaks down into drops, a video signal sourcesynchronized by sync signals applies its signals to the charging tunnelfor charging each drop formed therein, said charged ink drops passingout from the charging tunnel,

the improvement for establishing correct phase of formation of said inkdrops relative to the application of a video signal in said chargingtunnel comprising: video signal means for inhibiting every other twodrop charging signals applied to said charging tunnel from said videosignal source for charging the first two of each four drops and notcharging the last two of each four drops, detecting means positionedadjacent said charging tunnel for intercepting all of the ink dropspassing therethrough, said detecting means including transducer meansfor generating a signal in response to each drop received by saiddetecting means,

means connected to said tranducing means for detecting when thefrequency of each two signals from said transducer means has apredetermined value and for producing an output indicative thereof, and

means responsive to the absence of said output for changing the phase ofthe sync signals applied to said electromotive transducer to correct thephase of the drops which are formed to be in synchronism with signalsfrom said video sig nal source.

2. In a system for testing the phase of formation of drops in an inkdrop writing system by applying video signals at a predeterminedfrequency to a charging tunnel through which there passes an ink jetwhich is emitted from a nozzle vibrated at a frequency synchronized withthe frequency of said video signals for causing the ink jet to 8 breakinto drops within said charging tunnel, and there are means positioneddownstream of the exit from said charging tunnel for receiving said inkdrops, detecting from the frequency of said ink drops whether or notthey have been formed in phase with said video signals, the improvementcomprising:

means for generating video signals comprising a train of pulses havingthe same frequency as the frequency of the formation of said drops withevery other two pulses omitted from said train,

means for applying said video signals to said charging tunnel, and

a filter in said means for detecting having a pass frequency equal tothe frequency of the occurrence of said two adjacent pulses in saidvideo signal wave train.

3. In a system as recited in claim 2 wherein said means for generating avideo signal includes divider means connected to said sync signal sourceproviding a pulse train at one-fourth the frequency of said syncsignals, and means responsive to said dividing means for producing apulse train comprising two adjacent pulses for each pulse in a wavetrain output of said dividing means which are spaced from the succeedingtwo pulses by the interval required for two adjacent pulses.

4. In an ink drop writing system as recited in claim 3 wherein saidvideo signal means includes means connected to said source of syncsignals for producing video signals having a frequency which isone-fourth of said sync signals, and

means connected to said dividing means output for producing a videosignal pulse train wherein there are successive pairs of pulsesgenerated in response to each pulse received, which successive pairs ofpulses are spaced by an interval having the duration of a pair of saidpulses.

5. Apparatus as recited in claim 2 wherein said filter means is tuned tothe frequency of the repetition of the occurrence of each two chargeddrops.

References Cited UNITED STATES PATENTS 3,465,350 9/1969 Keur et al.346-75 3,465,351 9/1969 Keur et al. 34675 JOSEPH W. HARTARY, PrimaryExaminer

